Question 1

Which of the following statements best describes a zwitterion form of an amino acid at physiological pH?

Accepted Answer

The amino group is positively charged ($$\mathrm{NH_3$^+}) $$and the carboxyl group is negatively charged ($$\mathrm{COO^-}).$$

Question 2

Which of the following amino acids is classified as essential and must be obtained from the diet?

Accepted Answer

Leucine

Question 3

A patient is diagnosed with a genetic disorder that prevents the synthesis of phenylalanine. What dietary recommendation should be made?

Accepted Answer

Increase intake of foods rich in phenylalanine, as it is an essential amino acid.

Question 4

Which structural feature is common to all standard amino acids?

Accepted Answer

A carboxyl group, an amino group, a hydrogen atom, and a unique R group attached to the alpha carbon

Question 5

Which of the following best explains why amino acids are chiral (except glycine)?

Accepted Answer

The alpha carbon is attached to four different groups.

Question 6

Which of the following amino acids has a nonpolar side chain?

Accepted Answer

Valine

Question 7

Amino acids can be grouped based on the properties of their R group. Which group would lysine belong to?

Accepted Answer

Basic (positively charged)

Question 8

Which of the following correctly describes the formation of a peptide bond?

Accepted Answer

It is a covalent bond formed between the carboxyl group of one amino acid and the amino group of another, releasing water.

Question 9

Which of the following is true regarding the primary structure of a protein?

Accepted Answer

It is the linear sequence of amino acids linked by peptide bonds.

Question 10

A mutation changes a single amino acid in the beta chain of hemoglobin from glutamic acid to valine. What is the most likely consequence?

Accepted Answer

Formation of sickle-shaped red blood cells under low oxygen conditions.

Question 11

Which of the following best describes the secondary structure of proteins?

Accepted Answer

The spatial arrangement of local regions, such as alpha helices and beta sheets, stabilized by hydrogen bonds.

Question 12

Which amino acid is unique because its side chain forms a ring with the amino group, restricting its flexibility?

Accepted Answer

Proline

Question 13

Which of the following amino acids contains a sulfur atom in its side chain?

Accepted Answer

Methionine

Question 14

If a polypeptide contains 50 amino acids, what is the best classification for this molecule?

Accepted Answer

Oligopeptide

Question 15

Which of the following statements about essential and non-essential amino acids is correct?

Accepted Answer

Essential amino acids must be obtained from the diet because the body cannot synthesize them.

Question 16

Which of the following amino acids is most likely to be found at the active site of an enzyme that catalyzes acid-base reactions?

Accepted Answer

Aspartate

Question 17

Amino acids are classified based on the properties of their R group. Which property would you expect for the R group of glutamate?

Accepted Answer

Acidic (negatively charged)

Question 18

Which of the following best explains why glycine is not chiral?

Accepted Answer

Its R group is a hydrogen atom, so the alpha carbon is not attached to four different groups.

Question 19

Which of the following amino acids has an aromatic side chain?

Accepted Answer

Phenylalanine

Question 20

A protein is hydrolyzed completely. What are the resulting products?

Accepted Answer

Amino acids

Amino Acids: Structure, Classification, and Nutritional Importance

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